This invention relates to the field of antivirals and in particular to derivatives of acyclic nucleosides useful against herpes and retroviral infections. The invention provides novel compounds, pharmaceutical compositions comprising these compounds, methods for the treatment or prophylaxis of viral infections employing them, methods for their manufacture and novel intermediates.
The practical utility of many acyclic nucleosides is limited by their relatively modest pharmacokinetics. A number of prodrug approaches have been explored in an effort to improve the bioavailability of acyclic nucleosides in general. One of these approaches involves the preparation of ester derivatives, particularly aliphatic esters, of one or more of the hydroxy groups on the acyclic side chain.
European patent EP 165 289 describes the promising antiherpes agent 9-[4-hydroxy-(2-hydroxymethyl)butyl]guanine, otherwise known as H2G. European patent EP 186 640 discloses 6-deoxy H2G. European patent EP 343 133 discloses that these compounds, particularly the R-(xe2x88x92) enantiomer, are additionally active against retroviral infections such as HIV. Various derivatives of H2G, such as phosphonates, aliphatic esters (for example, the diacetate and the dipropionate) and ethers of the hydroxy groups on the acyclic side chain are disclosed in EP 343 133. This patent also discloses methods for the preparation of these derivatives comprising the condensation of the acyclic side chain to the N-9 position of a typically 6-halogenated purine moiety or, alternatively, the imidazole ring closure of a pyrimidine or furazano-[3,4-d]pyrimidine moeity or the pyrimidine ring closure of an imidazole moiety, where the acyclic side chain is already present in the precursor pyrimidine or imidazole moiety, respectively. In the broadest description of each of these methods the acyclic side chain is pre-derivatised but individual examples also show a one-step diacylation of H2G with acetic or proprionic anhydride and DMF.
Harnden, et al., J. Med. Chem. 32, 1738 (1989) investigated a number of short chain aliphatic esters of the acyclic nucleoside 9-[4-hydroxy-(3-hydroxymethyl)butyl]guanine, otherwise known as penciclovir, and its 6-deoxy analog. Famciclovir, a marketed antiviral agent, is the diacetyl derivative of 6-deoxy penciclovir.
Benjamin, et al., Pharm. Res. 4 No. 2, 120 (1987) discloses short chain aliphatic esters of 9-[(1,3-dihydroxy-2-propoxy)-methyl]guanine, otherwise known as ganciclovir. The dipropionate ester is disclosed to be the preferred ester.
Lake-Bakaar, et al., discloses in Antimicrob. Agents Chemother. 33 No. 1, 110-112 (1989) diacetate and dipropionate derivatives of H2G and monoacetate and diacetate derivatives of 6-deoxy H2G. The diacetate and dipropionate derivatives of H2G are reported to result in only modest improvements in bioavailability relative to H2G.
International patent application WO94/24134, published Oct. 27, 1994, discloses aliphatic ester prodrugs of the 6-deoxy N-7 analog of ganciclovir, including the di-pivaloyl, di-valeroyl, mono-valeroyl, mono-oleoyl and mono-stearoyl esters.
International patent application WO93/07163, published Apr. 15, 1993 and International patent application WO94/22887, published Oct. 13, 1994, both disclose mono-ester derivatives of nucleoside analogs derived from mono-unsaturated C18 or C20 fatty acids. U.S. Pat. No. 5,216,142, issued Jun. 1, 1993, also discloses long chain fatty acid mono-ester derivatives of nucleoside analogs.
A second approach to providing prodrugs of acyclic nucleosides involves the preparation of amino acid esters of one or more of the hydroxy groups on the acyclic side chain. European patent EP 99 493 discloses generally amino acid esters of acyclovir and European patent application EP 308 065, published Mar. 22, 1989, discloses the valine and isoleucine esters of acyclovir.
European patent application EP 375 329, published Jun. 27, 1990, discloses amino acid ester derivatives of ganciclovir, including the di-valine, di-isoleucine, di-glycine and di-alanine ester derivatives. International patent application WO95/09855, published Apr. 13, 1995, discloses amino acid ester derivatives of penciclovir, including the mono-valine and di-valine ester derivatives.
DE 19526163, published Feb. 1, 1996 and U.S. Pat. No. 5,543,414 issued Aug. 6, 1996, disclose achiral amino acid esters of ganciclovir.
European patent application EP 694 547, published Jan. 31, 1996, discloses the mono-L-valine ester of ganciclovir and its preparation from di-valyl-ganciclovir.
European patent application EP 654 473, published May 24, 1995, discloses various bis amino acid ester derivatives of 9-[1xe2x80x2,2xe2x80x2-bishydroxymethyl)-cyclopropan-1xe2x80x2yl]methylguanine.
International patent application WO95/22330, published Aug. 24, 1995, discloses aliphatic esters, amino acid esters and mixed acetate/valinate esters of the acyclic nucleoside 9-[3,3-dihydroxymethyl-4-hydroxy-but-1-yl]guanine. This reference discloses that bioavailability is reduced when one of the valine esters of the trivaline ester derivative is replaced with an acetate ester.
We have found that diester derivatives of H2G bearing specific combinations of an amino acid ester and a fatty acid ester are able to provide significantly improved oral bioavailability relative to the parent compound (H2G). In accordance with a first aspect of the invention there is thus provided novel compounds of the formula I 
where
a) R1 is xe2x80x94C(O)CH(CH(CH3)2)NH2 or xe2x80x94C(O)CH(CH(CH3)CH2CH3)NH2 and R2 is xe2x80x94C(O)C3-C21 saturated or monounsaturated, optionally substituted alkyl; or
b) R1 is xe2x80x94C(O)C3-C21 saturated or monounsaturated, optionally substituted alkyl and R2 is xe2x80x94C(O)CH(CH(CH3)2)NH2 or xe2x80x94C(O)CH(CH(CH3)CH2CH3)NH2; and
R3 is OH or H;
and pharmaceutically acceptable salts thereof
The advantageous effect on oral bioavailability of the mixed fatty acid and amino acid esters of the invention is particularly unexpected in comparison to the oral bioavailability of the corresponding fatty acid esters. Based on the results using a urinary recovery assay (Table 1A) or a plasma drug assay (Table 1B) of H2G from rats, neither the mono or di-fatty acid esters of H2G provide any improvement in oral bioavailability relative to the parent compound H2G. Indeed the di-stearate derivative provided significantly lower bioavailability than the parent indicating that a stearate ester may be detrimental for improving oral bioavailability of H2G. Converting one or both of the hydroxyls in certain other acyclic nucleoside analogues to the corresponding valine or di-valine ester has been reported to improve bioavailability. Conversion of H2G to the coresponding mono- or di-valyl ester derivatives produced similar improvement in bioavailability relative to the parent compound. Given that fatty acid derivatives of H2G are shown to be detrimental for improving bioavailability, it was unexpected that a mixed amino acid/fatty acid diester derivative of H2G would provide improved or comparable oral bioavailability to that of the valine diester derivative of H2G, based on urine recovery and plasma drug assays, respectively.
The invention also provides pharmaceutical compositions comprising the compounds of Formula I and their pharmaceutically acceptable salts in conjunction with a pharmaceutically acceptable carrier or diluent. Further aspects of the invention include the compounds of Formula I and their pharmaceutically acceptable salts for use in therapy and the use of these compounds and salts in the preparation of a medicament for the treatment or prophylaxis of viral infection in humans or animals.
The compounds of the invention are potent antivirals, especially against herpes infections, such as those caused by Varicella zoster virus, Herpes simplex virus types 1 and 2, Epstein-Barr virus, Herpes type 6 (HHV-6) and type 8 (HHV-8). The compounds are particularly useful against Varicella zoster virus infections such as shingles in the elderly including post herpetic neuralgia or chicken pox in the young where the duration and severity of the disease can be reduced by several days. Epstein Barr virus infections amenable to treatment with the compounds include infectious mononucleosis/glandular fever which has previously not been treatable but which can cause many months of scholastic incapacity amongst adolescents.
The compounds of the invention are also active against certain retroviral infections, notably SIV, HIV-1 and HIV-2, and against infections where a transactivating virus is indicated.
Accordingly a further aspect of the invention provides a method for the prophylaxis or treatment of a viral infection in humans or animals comprising the administration of an effective amount of a compound of Formula I or its pharmaceutically acceptable salt to the human or animal.
Advantageously group R3 is hydroxy or its tautomer xe2x95x90O so that the base portion of the compounds of the invention is the naturally occuring guanine, for instance in the event that the side chain is cleaved in vivo. Alternatively, R3 may be hydrogen thus defining the generally more soluble 6-deoxy derivative which can be oxidised in vivo (e.g. by xanthine oxidase) to the guanine form.
The compound of formula I may be present in racemic form, that is a mixture of the 2R and 2S isomers. Preferably, however, the compound of formula I has at least 70%, preferably at least 90% R form, for example greater than 95%. Most preferably the compound of formula I is enantiomerically pure R form.
Preferably the amino acid of group R1/R2 is derived from an L-amino acid.
Preferably the fatty acid of group R1/R2 has in total an even number of carbon atoms, in particular, decanoyl (C10), lauryl (C12), myristoyl (C14), palmitoyl (C16), stearoyl (C18) or eicosanoyl (C20). Other useful R1/R2 groups include butyryl, hexanoyl, octanoyl or behenoyl (C22). Further useful R1/R2 groups include those derived from myristoleic, myristelaidic, palmitoleic, palmitelaidic, n6-octadecenoic, oleic, elaidic, gandoic, erucic or brassidic acids. Monounsaturated fatty acid esters typically have the double bond in the trans configuration, preferably in the xcfx89-6, xcfx89-9 or xcfx89-11 position, dependent upon their length. Preferably the R1/R2 group is derived from a fatty acid which comprises a C9 to C17 saturated, or n:9 monounsaturated, alkyl.
The saturated or unsaturated fatty acid or R1/R2 may optionally be substituted with up to five similar or different substituents independently selected from the group consisting of such as hydroxy, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 alkoxy C1-C6 alkyl, C1-C6 alkanoyl, amino, halo, cyano, azido, oxo, mercapto and nitro, and the like.
Most preferred compounds of the formula I are those where R1 is xe2x80x94C(O)CH(CH3)2)NH2 or xe2x80x94C(O)CH(CH(CH3)CH2CH3)NH2 and R2 is xe2x80x94C(O)C9-C17 saturated alkyl.
The term xe2x80x9clower alkylxe2x80x9d as used herein refers to straight or branched chain alkyl radicals containing from 1 to 7 carbon atoms including, but not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl, n-pentyl, 1-methylbutyl, 2,2-dimethylbutyl, 2-methylpentyl, 2,2-dimethylpropyl, n-hexyl and the like.
The term xe2x80x9cN-protecting groupxe2x80x9d or xe2x80x9cN-protectedxe2x80x9d as used herein refers to those groups intended to protect the N-terminus of an amino acid or peptide or to protect an amino group against undesirable reactions during synthetic procedures. Commonly used N-protecting groups are disclosed in Greene, xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d (John Wiley and Sons, New York, 1981), which is hereby incorporated by reference. N-protecting groups include acyl groups such as formyl, acetyl, propionyl, pivaloyl, t-butylacetyl, 2-chloroacetyl, 2-bromoacetyl, trifluoracetyl, trichloroacetyl, phthalyl, o-nitrophenoxyacetyl, xcex1-chlorobutyryl, benzoyl, 4-chlorobenzoyl, 4-bromobenzoyl, 4-nitrobenzoyl, and the like; sulfonyl groups such as benzenesulfonyl, p-toluenesulfonyl, and the like, carbamate forming groups such as benzyloxycarbonyl, p-chlorobenzyloxycarbonyl, p-methoxybenzyloxycarbonyl, p-nitrobenzyloxycarbonyl, 2-nitrobenzyloxycarbonyl, p-bromobenzyloxycarbonyl, 3,4-dimethoxybenzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2-nitro-4,5-dimethoxybenzyloxycarbonyl, 3,4,5-trimethoxybenzyloxycarbonyl, 1-(p-biphenylyl)-1-methylethoxycarbonyl, xcex1,xcex1-dimethyl-3,5-dimethoxybenzyloxycarbonyl, benzhydryloxycarbonyl, t-butoxycarbonyl, diisopropylmethoxycarbonyl, isopropyloxycarbonyl, ethoxycarbonyl, methoxycarbonyl, allyloxycarbonyl, 2,2,2-trichloroethoxycarbonyl, phenoxycarbonyl, 4-nitrophenoxycarbonyl, fluorenyl-9-methoxycarbonyl, cyclopentyloxycarbonyl, adamantyloxycarbonyl, cyclohexyloxycarbonyl, phenylthiocarbonyl, and the like; alkyl gropus such as benzyl, triphenylmethyl, benzyloxymethyl and the like; and silyl groups such as trimethylsilyl and the like.
Favoured N-protecting groups include formyl, acetyl, benzoyl, pivaloyl, t-butylacetyl, phenylsulfonyl, benzyl, t-butoxycarbonyl (BOC) and benzyloxycarbonyl (Cbz).
The term xe2x80x9cactivated ester derivativexe2x80x9d as used herein refers to acid halides such as acid chlorides, and activated esters including, but not limited to, formic and acetic acid derived anhydrides, anhydrides derived from alkoxycarbonyl halides such as isobutyloxycarbonylchloride and the like, N-hydroxysuccinimide derived esters, N-hydroxyphthalimide derived esters, N-hydroxybenzotriazole derived esters, N-hydroxy-5-norbomene-2,3-dicarboxamide derived esters, 2,4,5-trichlorophenyl derived esters and the like.
Preferred compounds of formula I include:
(R)-9-[2-(butyryloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[2-(4-acetylbutyryloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[2-(hexanoyloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(octanoyloxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(decanoyloxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(dodecanoyloxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(tetradecanoyloxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(hexadecanoyloxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-(octadecanoyloxymethyl)butyl]guanine,
(R)-9-[2-(eicosanoyloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[2-(docosanoyloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-((9-tetradecenoyl)oxymethyl)butyl]guanine,
(R)-9-[2-((9-hexadecenoyl)oxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-((6-octadecenoyl)oxymethyl)butyl]guanine,
(R)-9-[4-(L-isoleucyloxy)-2-((9-octadecenoyl)oxymethyl)-butyl]guanine,
(R)-9-[2-((11-eicosanoyl)-oxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[2-((13-docosenoyl)-oxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-2-amino-9-[2-(butyryloxymethyl)-4-(L-isoleucyloxy)butyl]purine,
R)-2-amino-9-[2-(4-acetylbutyryloxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[2-(hexanoyloxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(octanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(decanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(dodecanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(decanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(hexadecanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(octadecanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(eicosanoyloxymethyl)butyl]purine,
(R)-2-amino-9-[2-(eicosanoyloxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[2-(docosanoyloxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-((9-tetradecenoyl)oxymethyl)butyl]purine,
(R)-2-amino-9-[2-((9-hexadecenoyl)oxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-((6-octadecenoyl)oxymethyl)butyl]purine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-((9-octadecenoyl)oxymethyl)butyl]purine,
(R)-2-amino-9-[2-((11-eicosanoyl)oxymethyl)-4-(L-isoleucyloxy)butyl]purine, or
(R)-2-amino-9-[2-((13-docosenoyl)oxymethyl)-4-(L-isoleucyloxy)butyl]purine,
and their pharmaceutically accepable salts.
Further preferred compounds include:
(R)-9-[2-(butyryloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(4-acetylbutyryloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(hexanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(octanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(decanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(dodecanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(tetradecanoyloxymethyl-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-hexadecanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(octadecanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(eicosanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(eicosanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-(docosanoyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-((9-tetradecenoyl)oxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-((9-hexadecenoyl)oxymethyl)-4-(L-valyloxy)butyl]guanne,
(R)-9-[2-((6-octadecenoyl)oxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-((9-octadecenoyl)oxymethyl)-4-(L-valyloxy)-butyl]guanine,
(R)-9-[2-((11-eicosanoyl)oxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-((13-docosenoyl)oxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-2-amino-9-[2-(butyryloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(4-acetylbutyryloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(hexanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(octanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(decanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(dodecanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(tetradecanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(hexadecanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(octadecanoyloxymethyl)-4-(L-valyloxy)-butyl]purine,
(R)-2-amino-9-[2-(eicosanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-(docosanoyloxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-((9-tetradecenoyl)oxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-((9-hexadecenoyl)oxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-((6-octadecenoyl)oxymethyl)-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-((9-octadecenoyl)oxymethyl)-4-(L-valyloxy)-butyl]purine,
(R)-2-amino-9-[2-((11-eicosenoyl)-oxymethyl)-4-(L-valyloxy)butyl]purine, or
(R)-2-amino-9-[2-((13-docosenoyl)-oxymethyl)-4-(L-valyloxy)butyl]purine;
and their pharmaceutically acceptable salts.
Other preferred compounds of formula I include:
(R)-9-[4-(butyryloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(4-acetylbutyryloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(hexanoyloxy)-2-(L-valyloxy methyl)butyl]guanine,
(R)-9-[4-(octanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(decanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(dodecanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(tetradecanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-hexadecanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(octadecanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(eicosanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-(docosanoyloxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-((9-tetradecenoyl)oxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-((9-hexadecenoyl)oxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-((6-octadecenoyl)oxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-((9-octadecenoyl)oxy)-2-(L-valyloxymethyl)-butyl]guanine,
(R)-9-[4-((11-eicosenoyl)oxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-9-[4-((13-docosenoyl)-oxy)-2-(L-valyloxymethyl)butyl]guanine,
(R)-2-amino-9-[4-(butyryloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(4-acetylbutyryloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(hexanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(octanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(decanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(dodecanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(tetradecanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(hexadecanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(octadecanoyloxy)-2-(L-valyloxymethyl)-butyl]purine,
(R)-2-amino-9-[4-(eicosanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-(docosanoyloxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-((9-tetradecenoyl)oxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-((9-hexadecenoyl)oxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-((6-octadecenoyl)oxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-((9-octadecenoyl)oxy)-2-(L-valyloxymethyl)butyl]purine,
(R)-2-amino-9-[4-((11-eicosenoyl)oxy)-2-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-((13-docosenoyl)oxymethyl)-2-(L-valyloxy)butyl]purine, or
and their pharmaceutically acceptable salts.
The compounds of formula I can form salts which form an additional aspect of the invention. Appropriate pharmaceutically acceptable salts of the compounds of formula I include salts of organic acids, especially carboxylic acids, including but not limited to acetate, trifluoroacetate, lactate, gluconate, citrate, tartrate, maleate, malate, pantothenate, isethionate, adipate, alginate, aspartate, benzoate, butyrate, digluconate, cyclopentanate, glucoheptanate, glycerophosphate, oxalate, heptanoate, hexanoate, fumarate, nicotinate, palmoate, pectinate, 3-phenylpropionate, picrate, pivalate, proprionate, tartrate, lactobionate, pivolate, camphorate, undecanoate and succinate, organic sulphonic acids such as methanesulphonate, ethanesulphonate, 2-hydroxyethane sulphonate, camphorsulphonate, 2-napthalenesulphonate, benzenesulphonate, p-chlorobenzenesulphonate and p-toluenesulphonate; and inorganic acids such as hydrochloride, hydrobromide, hydroiodide, sulphate, bisulphate, hemisulphate, thiocyanate, persulphate, phosphoric and sulphonic acids. Hydrochloric acid salts are convenient.
The compounds of Formula I may be isolated as the hydrate. The compounds of the invention may be isolated in crystal form, preferably homogenous crystals, and thus an additional aspect of the invention provides the compounds of Formula I in substantially pure crystalline form, comprising  greater than 70%, preferably  greater than 90% homogeneous crystalline material for example  greater than 95% homogeneous crystalline material.
The compounds of the invention are particularly suited to oral administration, but may also be administered rectally, vaginally, nasally, topically, transdermally or parenterally, for instance intramuscularly, intravenously or epidurally. The compounds may be administered alone, for instance in a capsule, but will generally be administered in conjunction with a pharmaceutically acceptable carrier or diluent. The invention extends to methods for preparing a pharmaceutical composition comprising bringing a compound of Formula I or its pharmaceutically acceptable salt in conjunction or association with a pharmaceutically acceptable carrier or vehicle.
Oral formulations are conveniently prepared in unit dosage form, such as capsules or tablets, employing conventional carriers or binders such as magnesium stearate, chalk, starch, lactose, wax, gum or gelatin. Liposomes or synthetic or natural polymers such as HPMC or PVP may be used to afford a sustained release formulation. Alternatively the formulation may be presented as a nasal or eye drop, syrup, gel or cream comprising a solution, suspension, emulsion, oil-in-water or water-in-oil preparation in conventional vehicles such as water, saline, ethanol, vegetable oil or glycerine, optionally with flavourant and/or preservative and/or emulsifier.
The compounds of the invention may be administered at a daily dose generally in the range 0.1 to 200 mg/kg/day, advantageously, 0.5 to 100 mg/kg/day, more preferably 10 to 50 mg/kg/day, such as 10 to 25 mg/kg/day. A typical dosage rate for a normal adult will be around 50 to 500 mg, for example 300 mg, once or twice per day for herpes infections and 2 to 10 times this dosage for HIV infections.
As is prudent in antiviral therapy, the compounds of the invention can be administered in combination with other antiviral agents, such as acyclovir, valcyclovir, penciclovir, famciclovir, ganciclovir and its prodrugs, cidofovir, foscamet and the like for herpes indications and AZT, ddI, ddC, d4T, 3TC, foscarnet, ritonavir, indinavir, saquinavir, delaviridine, Vertex VX 478, Agouron AG1343 and the like for retroviral indications.
The compounds of the invention can be prepared de novo or by esterification of the H2G parent compound which is prepared, for example, by the synthesis methodology disclosed in European Patent EP 343 133, which is incorporated herein by reference.
A typical reaction scheme for the preparation of H2G is depicted overleaf: 
The condensation in step 1 is typically carried out with a base catalyst such as NaOH or Na2CO3 in a solvent such as DMF. Step 2 involves a reduction which can be performed with LiBH4/tetrahydrofuran in a solvent such as t-BuOH. The substitution in step 3 of the chlorine with an amino group can be performed under pressure with ammonia. Step 4 employs adenosine deaminase which can be conveniently immobilized on a solid support. Cooling the reaction mixture allows unreacted isomeric precursor to remain in solution thereby enhancing purity.
Starting materials for compounds of the invention in which R3 is hydrogen may be prepared as shown in European Patent EP 186 640, the contents of which are incorporated herein by reference. These starting materials may be acylated as described for H2G below, optionally after protecting the purine 2-amino group with a conventional N-protecting group as defined above, especially BOC (t-BuOxe2x80x94COxe2x80x94), Z (BnOxe2x80x94COxe2x80x94) or Ph3Cxe2x80x94.
The compounds of the invention may be prepared from H2G as described below in Schemes A and B.
A. Direct Acylation Method 
Scheme A depicts the preparation of compounds in which R1 is derived from the amino acid and R2 is derived from the fatty acid, but the converse scheme is applicable to compounds where R1 is derived from the fatty acid and R2 is derived from the amino acid ester. In the variant specifically depicted in scheme A above, G is guanine or 6-deoxyguanine, PG is an optional N-protecting group or hydrogen, R1* is the valine or isoleucine side chain and R2* is the fatty acid chain. H2G is depicted above as a starting material but this of course may be optionally protected at R3 or the 2 position of the purine with conventional N-protecting groups (not shown). The H2G (derivative) reacts in the first step with an activated R1 xcex1-amino acid derivative, as further described below, in a solvent such as dimethylformamide or pyridine, to give a monoacylated product. The R1 xcex1-amino acid may be suitably N-protected with N-BOC or N-CBz or the like. Under controlled conditions, the first acylation can be made to predominantly take place at the side chain 4-hydroxy group on the side chain of H2G. These controlled conditions can be achieved, for example, by manipulating the reagent concentrations or rate of addition, especially of the acylating agent, by lowering the temperature or by the choice of solvent. The reaction can be followed by TLC to monitor the controlled conditions.
After purification, the R1 monoacylated compounds are further acylated on the side chain 2xe2x80x94CH2OH group with the appropriate activated fatty acid derivative to give diacylated products using similar procedures as for the first esterification step. The diester products are subsequently subjected to a conventional deprotection treatment using for example trifluoroacetic acid, HCl(aq)/dioxane or hydrogenation in the presence of catalyst to give the desired compound of Formula I. The compound may be in salt form depending on the deprotection conditions.
The activated R1/R2 acid derivative used in the various acylations may comprise e.g. the acid halide, acid anhydride, activated acid ester or the acid in the presence of coupling reagent, for example dicyclohexylcarbodiimide, where xe2x80x9cacidxe2x80x9d in each case represents the corresponding R1/R2 amino acid or the R1/R2 fatty acid. Representative activated acid derivatives include the acid chloride, formic and acetic acid derived mixed anhydrides, anhydrides derived from alkoxycarbonyl halides such as isobutyloxycarbonylchloride and the like, N-hydroxysuccinamide derived esters, N-hydroxyphthalimide derived esters, N-hydroxy-5-norbomene-2,3-dicarboxamide derived esters, 2,4,5-trichlorophenol derived esters and the like.
B. Via Protection of the Side Chain 4-Hydroxy Group 
wherein G, PG, R1* and R2* are as described for scheme A.
Scheme B has been exemplified with reference to the preparation of a compound where R1 is derived from an amino acid and R2 is derived from the fatty acid ester, but a converse scheme will be applicable to compounds where R2 is derived from the amino acid and R1 is derived from the fatty acid. This scheme relies on regioselective protection of the H2G side chain 4-hydroxy group with a bulky protecting group. In scheme B above this is depicted as t-butyldiphenylsilyl, but other regioselective protecting groups such as trityl, 9-(9-phenyl)xanthenyl, 1,1-bis(4-methylphenyl)-1xe2x80x2-pyrenylmethyl may also be appropriate. The resulting product is acylated at the side chain 2-hydroxymethyl group using analogous reagents and procedures as described in scheme A above, but wherein the activated acid derivative is the R2 fatty acid, for example, myristic, stearic, oleic, elaidic acid chloride and the like. The thus monoacylated compounds are subjected to appropriate deprotection treatment to remove the side chain 4-hydroxy protecting group which can be done in a highly selective manner with such reagents, depending on the regioselective protecting group, as HF/pyridine and the like and manipulation of the reaction conditions, viz reagent concentration, speed of addition, temperature and solvent etc, as elaborated above. The then free side chain 4-hydroxy group is acylated with the activated xcex1-amino acid in a similar way as described in scheme A above.
Additional techniques for introducing the amino acid ester of R1/R2, for instance in schemes A, B, C or D herein include the 2-oxa-4-aza-cycloalkane-1,3-dione method described in international patent application no. WO 94/29311.
Additional techniques for introducing the fatty acid ester of R1/R2, for instance in schemes A, B, C or D herein include the enzymatic route described in Preparative Biotransformations 1.11.8 (Ed S M Roberts, J Wiley and Son, NY, 1995) with a lipase such as SP 435 immobilized Candida antarcticus (Novo Nordisk), porcine pancreatic lipase or Candida rugosa lipase. Enzymatic acylation is especially convenient where it is desired to avoid N-protection and deprotection steps on the other acyl group or the purine 2-amine.
An alternative route to compounds of Formula I in which R3 is hydrogen is to 6-activate the correponding guanine compound of Formula I (wherein the amino acid ester moiety of R1/R2 is optionally protected with conventional N-protecting groups such as BOC) with an activating group such as halo. The thus activated 6-purine is subsequently reduced to purine, for instance with a palladium catalyst and deprotected to the desired 6-deoxy H2G di-ester.
A further aspect of the invention thus provides a method for the preparation of the compounds of formula I comprising
a) optionally N-protecting the purine 2 and/or 6 positions of a compound of formula I wherein R1 and R2 are each hydrogen;
b) regioselectively acylating the compound of Formula 1 at the side chain 4-hydroxy group with either
i) an optionally N-protected valine or isoleucine group,
ii) an optionally substituted, saturated or monounsaturated C3-C21COOH derivative, or
iii) a regioselective protecting group;
c) acylating at the side chain 2-hydroxymethyl group with
i) an optionally N-protected valine or isoleucine derivative, or
ii) an optionally substituted, saturated or monounsaturated C3-C21COOH derivative;
d) replacing the regioselective protecting group at R1, if present, with
i) an optionally N-protected valine or isoleucine derivative; or
ii) an optionally substituted, saturated or monounsaturated C3-C21COOH derivative; and
e) deprotecting the resulting compound as necessary.
Schemes A and B above employ selective acylation to stepwise add the amino acid and fatty acid esters. An alternative process for the preparation of the compounds of formula I starts with a diacylated H2G derivative, wherein both the acyl groups are the same, and employs selective removal of one of the acyl groups to obtain a monoacyl intermediate which is then acylated with the second, differing, acyl group in the same manner as Schemes A and B above.
Accordingly a further aspect of the invention provides a method for the preparation of a compound of the formula I, as defined above, which method comprises
A) the monodeacylation of a diacylated compound corresponding to formula I wherein R1 and R2 are both a valyl or isoleucyl ester (which is optionally N-protected) or are R1 and R2 are both xe2x80x94C(xe2x95x90O)C3-C21 saturated or monounsaturated, optionally substituted alkyl; and
B) acylating the thus liberated side chain 4-hydroxy or side chain 2-hydroxymethyl group with the corresponding valyl, isoleucyl or xe2x80x94C(xe2x95x90O)C3-C21 saturated or monounsaturated, optionally substituted alkyl; and
C) deprotecting as necessary.
This alternative process has the advantage that the preparation of the diacylated H2G derivative is facile and requires little or no purification steps. Selective removal of one only of the acyl groups of a diacylated H2G derivative can be achieved by manipulating the reaction conditions, in particular the temperature, rate of reactant addition and choice of base.
Compounds amenable to this alternative synthesis route are thus of the formula: 
where R1 and R2 are valyl or isoleucyl (which are optionally N-protected) or a xe2x80x94C(xe2x95x90O)C3-C21 saturated or monounsaturated, optionally substituted alkyl; and R3 is OH or H.
For ease of synthesis in this alternative route, it is preferred that R1 and R2 are both initially identical and are most preferably the same amino acid ester. Such a di-amino acid ester will generally be N-protected during its preparation and may be used directly in this condition in the selective deacylation step. Alternatively, such an N-protected di-aminoacylated H2G derivative may be deprotected and optionally reprotected, as described below. The unprotected di-aminoacyl H2G derivative thus comprises one of the following compounds:
(R)-9-[2-(L-isoleucyloxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[2-(L-valyloxymethyl)-4-(L-valyloxy)butyl]guanine,
(R)-2-amino-9-[4-(L-isoleucyloxy)-2-(L-isoleucyloxymethyl)butyl]purine, and
(R)-2-amino-9-[4-(L-valyloxy)-2-(L-valyloxymethyl)butyl]purine.
These unprotected H2G diacylated derivatives can be directly subject to selective deacylation of one of the acyl groups (typically the side chain 4-position acyl) followed by enzymatic acylation of the liberated 4-hydroxy as described above. Alternatively, the unprotected H2G diacylated derivative can be re-protected and then subjected to the selective deacylation, followed in turn by conventional acylation with the fatty acid ester, as described in Schemes A and B. Conveniently, such a reprotection step is done with a different N-protecting group, having properties appropriate to the subsequent acylation. For example, it is convenient to employ a lipophilic N-protecting group, such as Fmoc when preparing a di-amino acid H2G derivative, as the lipophilic nature of the protecting group assists with separation of the acylated products. On the other hand, the lipophilic nature of Fmoc is of less utility when conducting an acylation with a fatty acid, and thus it is convenient to reprotect a diacylated H2G with an alternative N-protecting group such as BOC.
It will also be apparent that the preparation of the compounds of formula I can commence with the novel monoacylated intermediates of step b i), ii) or iii) in the above defined first method aspect of the invention. These compounds are thus of the formula: 
where one of R1 and R2 is
i) xe2x80x94C(O)CH(CH(CH3)2)NH2 or xe2x80x94C(O)CH(CH(CH3)CH2CH3)NH2 
ii) a xe2x80x94C(xe2x95x90O)C3-C21 saturated or monounsaturated, optionally substituted alkyl, or
iii) a regioselective protecting group;
the other of R1 and R2 is hydrogen; and
R3 is OH or H;
Useful compounds thus include:
(R)-9-[2-hydroxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(trityloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(9-(9-phenyl)xanthenyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(1,1-bis(4-methylphenyl)-1xe2x80x2-pyrenylmethyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(decanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl)-4-(dodecanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(tetradecanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl)-4-(hexadecanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(octadecanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl)-4-(eicosanoyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(docosanoyloxy)butyl]guanine,
(R)-9-[4-hydroxy-2-(decanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(dodecanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(tetradecanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(hexadecanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(octadecanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(eicosanoyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(docosanoyloxymethyl)butyl]guanine,
(R)-9-[2-hydroxymethyl-4-(L-valyloxy)butyl]guanine,
(R)-9-[2-hydroxymethyl)-4-(L-isoleucyloxy)butyl]guanine,
(R)-9-[4-hydroxy-2-(L-isoleucyloxymethyl)butyl]guanine,
(R)-9-[4-hydroxy-2-(L-valyloxymethyl)butyl]guanine.
(R)-2-amino-9-[2-hydroxymethyl-4-(L-valyloxy)butyl]purine,
(R)-2-amino-9-[2-hydroxymethyl)-4-(L-isoleucyloxy)butyl]purine,
(R)-2-amino-9-[4-hydroxy-2-(L-isoleucyloxymethyl)butyl]purine, and
(R)-2-amino-9-[4-hydroxy-2-(L-valyloxymethyl)butyl]purine.
Regioselectively protected, sidechain 4-hydroxy intermediates from step c) of the above described first method aspect of the invention are also novel compounds.
Useful compounds thus include:
(R)-9-[2-decanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-dodecanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-tetradecanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-hexadecanoyloxymethyl-4-(t-butyldiphenylchlorosilane)butyl]guanine,
(R)-9-[2-octadecanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-eicosanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
(R)-9-[2-docosanoyloxymethyl-4-(t-butyldiphenylsilyl)butyl]guanine,
An alternative process for the preparation of compounds of the invention of the formula I wherein R3 is xe2x80x94OH is shown in Scheme C. 
Referring to Scheme C, malonate 1 (R4 and R5 are lower alkyl or benzyl or the like) is alkylated by reaction with from about 0.5 to about 2.0 molar equivalents of acetal 2 (R6 and R7 are lower alkyl or benzyl and the like or R6 and R7 taken together are xe2x80x94CH2CH2xe2x80x94 or xe2x80x94CH2CH2CH2xe2x80x94 or xe2x80x94CH2CH2CH2CH2xe2x80x94 and X1 is a leaving group (for example, Cl, Br or I, or a sulfonate such as methanesulfonate, triflate, p-toluenesulfonate, benzenesulfonate and the like)) in the presence of from about 0.5 to about 2.0 molar equivalents of a base (for example, potassium t-butoxide or sodium ethoxide or NaH or KH and the like) in an inert solvent (for example, DMF or THF or dioxane or dioxolane or N-methylpyrrolidone and the like) at a temperature of from about xe2x88x9240xc2x0 C. to about 190xc2x0 C. to provide alkylated malonate 3.
Reduction of 3 with from about 0.5 to about 4.0 molar equivalents of an ester to alcohol reducing agent (for example, LiBH4 or Ca(BH4)2 or NaBH4 or LiAlH4 and the like) in an inert solvent (for example, THF or methyl t-butyl ether or t-BuOH and the like) at a temperature of from about xe2x88x9220xc2x0 C. to about 100xc2x0 C. provides diol 4. Enzymatic esterification of 4 by reaction with from about 1.0 to about 20.0 molar equivalents of a vinyl ester 5 (R8 is C3-C21 saturated or monounsaturated, optionally substituted alkyl) in the presence of a lipase (for example, Lipase PS-30 or Lipase PPL or Lipase CCL and the like) or a phospholipase (for example phospholipase D and the like) provides the desired stereoisomer of ester 6. This reaction can be carried out in the absence of solvent or in the presence of an inert solvent (for example, methyl t-butyl ether or toluene or hexane and the like). The reaction is carried out at a temperature of from about xe2x88x9220xc2x0 C. to about 80xc2x0 C.
The alcohol substituent of 6 is converted to a leaving group (for example, a halogen or a sulfonate) by reaction with a halogenating agent (for example NBS/P(Ph)3 or NCS/P(Ph)3 or POCl3 or NCS/P(Ph)3/Nal in acetone and like) in an inert solvent (for example, methylene chloride or toluene or ethylacetate and the like) or by reaction with from about 0.8 molar equivalents to about 2.0 molar equivalents of a sulfonyl halide (for example, benzenesulfonylchloride, toluenesulfonylchloride or methane sulfonylchloride and the like) in the presence of from about 1.0 to about 4.0 molar equivalents of a base (for example, triethylamine or potassium carbonate or pyridine or dimethylaminopyridine or ethyldiisopropylamine and the like) in an inert solvent (for example methylene chloride or toluene or ethylacetate or pyridine or methyl t-butyl ether and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 100xc2x0 C. to provide ester 7. (X2 is a halogen or sulfonate leaving group).
Reaction of 7 with from about 0.9 to about 2.0 molar equivalents of 2-amino-4-chloropurine 8 in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example, potassium carbonate or NaH or KH or NaOH or KOH or lithium diisopropylamide and the like) in an inert solvent (for example, DMF or THF or acetonitrile or N-methylpyrrolidone or ethanol and the like) at a temperature of from about xe2x88x9225 xc2x0 C. to about 140xc2x0 C. provides substituted purine 9.
Alternatively Mitsunobu coupling (for example P(Ph)3/diethyl azidocarboxylate) of alcohol 6 with 2-amino-4-chloropurine 8 provides 9.
Reaction of 9 with from about 2.0 to about 20 molar equivalents of an alcohol R9OH (R9 is an alcohol protecting group such as benzyl and the like) in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example, potassium t-butoxide or potassium carbonate or NaH or KH or lithium diisopropylamide and the like) in an inert solvent (for example, THF or DMF and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 150xc2x0 C. provides alcohol 10.
Removal of the alcohol protecting group R9 of 10 (for example, by catalytic hydrogenation in an inert solvent such as ethanol or benzyl alcohol or methanol or THF and the like in the presence of an hydrogenation catalyst such as Pd/C or Pd(OH)2 and the like) provides substitued guanine 11.
Esterification of 11 by reaction with a) from about 0.8 to about 2.0 molar equivalents of (for example THF or DMF and the like) or b) from about 0.8 to about 2.0 molar equivalents of an activated derivative of R10COOH (for example, the acid chloride or N-hydroxysuccinimide ester or R10C(O)OC(O)R10 and the like) in the presence of from about 0 to about 3.0 molar equivalents of a base (for example, pyridine or triethylamine or ethyldiisopropylamine or DBU or potassium carbonate and the like) in an inert solvent (for example, methylene chloride or THF or pyridine or acetonitrile or DMF and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 100xc2x0 C. provides ester 12.
The acetal substituent of 12 is deprotected and the resulting aldehyde is reduced by first reacting 12 with from about 0.1 to about 10.0 molar equivalents of an acid (for example, triflic acid or HCl or acetic acid or sulfuric acid and the like) in an inert solvent (for example, THF/H2O or methylene chloride/H2O or ethylacetate/H2O or ethanol/H2O or methanol/H2O and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 100xc2x0 C. To the crude reaction mixture is added from about 0.1 to about 10.0 molar equivalents of a base (for example, sodium bicarbonate or potassium carbonate or triethylamine or pyridine or KOH and the like), additional inert solvent (for example, THF and or methylene chloride or ethylacetate or methyl t-butyl ether or isopropoanol and the like) and from about 0.3 to about 5.0 molar equivalents of an aldehyde reducing agent (for example, sodium borohydride or RaNi/H2 and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 100xc2x0 C. to provide alcohol 13.
Reaction of 13 with from about 0.8 to about 3.0 molar equivalents of N-protected amino acid P1NHCH(R11)COOH or an activated derivative thereof (P1 is an N-protecting group and R11 is isopropyl or isobutyl) in an inert solvent (for example, THF or dioxane or dioxolane or DMF or methylene chloride and the like) at a temperature of from about 25xc2x0 C. to about 100xc2x0 C. provides alcohol 14. N-deprotection of 14 provides the compound of the invention of formula I wherein R3 is xe2x80x94OH.
Alternatively compound 13 can be reacted with the symmetrical anhydride derived from P1NHCH(R11)COOH (i.e.P1NHCH(R11)C(O)Oxe2x80x94C(O)CH(R11)NHP1) to provide 1 wherein R3 is OH.
Another alternative process for the preparation of compounds wherein R3 is xe2x80x94OH is shown in Scheme D. 
Malonate 1 (R4 and R5 are lower alkyl or benzyl and the like) is alkylated with from about 0.5 to about 2.0 molar equivalents of ether 15 wherein X1 is a leaving group (for example Cl, Br of I, or a sulfonate such as methane sulfonate, triflate, p-toluenesulfonate, benzenesulfonate and the like) and R12 is xe2x80x94CH(Ph)2, xe2x80x94C(Ph)3 or xe2x80x94Si(t-Bu)(Me)2 and the like (Ph=phenyl) in the presence of from about 0.5 to about 2.0 molar equivalents of a base (for example potassium t-butoxide or sodium ethoxide or NaH or KH and the like) in an inert solvent (for example DMF or THF or dioxane or dioxolane or N-methyl pyrrolidinone and the like) at a temperature of from about xe2x88x9240xc2x0 C. to about 190xc2x0 C. to provide alkylated malonate 16.
Reduction of 16 with from about 0.5 to about 4.0 molar equivalents of an ester to alcohol reducing agent (for example LiBH4 or Ca(BH4)2 or NaBH4 or LiAlH4 and the like) in an inert solvent (for example THF or methyl t-butyl ether or ethanol or t-butanol and the like) at a temperature of from about xe2x88x9220xc2x0 C. to about 100xc2x0 C. provides diol 17. Enzymatic esterification of 17 by reaction with from about 1.0 to about 20.0 molar equivalents of a vinyl ester 5 (R8 is C3-C21 saturated or monounsaturated, optionally substituted alkyl) in the presence of a lipase (for example, Lipase PS-30 of Lipase PPL or Lipase CCL and the like) or a phospholipase (for example phospholipase D and the like) provides the desired stereoisomer of ester 18. The reaction can be carried out in the absence of solvent or in the presence of an inert solvent (for example methyl t-butyl ether or toluene or hexane or the like). The reaction is carried out at a temperature of from about xe2x88x9220xc2x0 C. to about 80xc2x0 C.
The alcohol sustituent of 18 is converted to a leaving group (for example a halogen or sulfonate) by reaction with a halogenating agent (for example NBS/P(Ph)3 or NCS/P(Ph)3 or POCl3 or NCS/P(Ph)3/Nal in acetone and the like) in an inert solvent (for example methylene chloride or toluene or ethylacetate and the like) or by reaction with from about 0.8 molar equivalents to about 2.0 molar equivalents of a sulfonyl halide (for example benzenesulfonylchloride, toluenesulfonylchloride or methane sulfonylchloride and the like) in the presence of from about 1.0 to about 4.0 molar equivalents of a base (for example triethylamine or potassium carbonate or pyridine or methyl t-butyl ether and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 100xc2x0 C. to provide ester 19. (X2 is a halogen or sulfonate leaving group).
Reaction of 19 with from about 0.9 to about 2.0 molar equivalents of 2-amino-4-chloropurine 8 in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example potassium carbonate or NaH or KH or NaOH or KOH or lithium diisopropylamide and the like) in an inert solvent (for example DMF or THF or acetonitrile or N-methylpyrrolidone or ethanol and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 140xc2x0 C. provides substituted purine 20.
Alternatively, Mitsunobu coupling (for example, P(PH)3/diethyl azidocarboxylate) of alcohol 18 with 2-amino-4-chloropurine 8 provides 20.
Reaction of 20 with from about 2.0 to about 20.0 molar equivalents of an alcohol R9OH (R9 is an alcohol protecting group such as benzyl and the like) in the presence of from about 1.0 to about 6.0 molar equivalents of a base (for example, potassium t-butoxide or potassium carbonate or NaH or KH or lithium diisopropylamide and the like in an inert solvent (for example, THF or DMF and the like) at a temperature of from about xe2x88x9225xc2x0 C. to about 150xc2x0 C. provides alcohol 21.
Removal of the alcohol protecting group R9 of 21 (for example by catalytic hydrogenation in an inert solvent such as ethanol or benzyl alcohol or methanol or THF and the like in the presence of an hydrogenation catalyst such as Pd/C or Pd(OH)2 and the like) provides substituted guanine 22.
The ether substitutent of 23 is deprotected by reaction with a) a reducing agent (for example, HCO2H and Pd/C and the like) wherein R12 is xe2x80x94CH(Ph)2 or xe2x80x94C(Ph)3, or b) a desilylating agent (for example Bu4NF and the like) wherein R12 is xe2x80x94Si(t-Bu)(Me)2 and the like to provide 13.
Alcohol 13 can be converted to 1 as outlined in scheme C.
An additional alternative involves enzymatic esterification of alcohol 4 or 17 with the vinyl ester CH2=CHxe2x80x94OC(O)R10 (i.e. R8=R10 in Schemes C and D) to directly incorporate into 6 or 18 the desired carboxylic acid ester of the final product I. This allows the elimination of the ester hydrolysis and reesterification involved in going from 9 to 12 or from 20 to 23.
The processes of Schemes C and D are characterized by the fact that each of the hydroxyl groups of the acyclic side chain is differentiated by the use of different hydroxy protecting groups or precursor groups. This allows the selective acylation of each of the hydroxy groups with either an amino acid or a fatty acid group.
Schemes C and D have been illustrated and described with reference to embodiments of the invention wherein R1 is derived from an amino acid and R2 is derived from a fatty acid. However, it will be apparent that respective converse schemes will apply to compounds where R1 is derived from a fatty acid and R2 is derived from an amino acid.
The invention will now be illustrated by way of example only with reference to the following non-limiting Examples, comparative examples and the accompanying Figures, in which: